Presently marine-seismic data are gathered and recorded essentially by means of ship-towed streamers. Preferably, the ship moves in parallel paths over the region to be surveyed. At the ends of the paths, the ship can be turned around and moved in the reverse direction parallel to and a distance from the previous path over the region being surveyed.
The course reversals at the ends of the paths are time-consuming and therefore expensive, and furthermore no data can be collected during the reversing time.
A number of different path patterns have been suggested to avoid the path reversals, whereby the reversal lengths are shortened. U.S. Pat. No. 4,486,863 discloses a method wherein a streamer is moved over the region being investigated along circles offset along an advancing line. The towing ship moves along circular paths and the streamer follows this path relatively precisely. To get from one circle to the next, the moment its course is parallel to the direction of advance of the circles to be covered, the ship leaves tangentially the already surveyed circle and again tangentially moves onto the next one, which then is again traversed completely, etc.
The above method is suitable only for surveying a large, continuous and uninterrupted region and allows avoiding reversal paths that do not contribute to data collection.
The "areal seismology" discussed above is no longer readily suitable when obstacles such as islands prevent surveying a continuous surface. It is precisely the immediate surroundings of a very small island which may be especially significant seismology. As will be recognized, the term "surveying" as used herein involves the process of transmitting sound energy, receiving energy reflected from subsurface formations and recording that information. It can, and often does, include processing of the collected data.